Hollow nanoparticles synthesized via Ostwald ripening and their upconversion luminescence-mediated Boltzmann thermometry over a wide temperature range

Upconversion nanoparticles (UCNPs) with hollow structures exhibit many fascinating optical properties due to their special morphology. However, there are few reports on the exploration of hollow UCNPs and their optical applications, mainly because of the difficulty in constructing hollow structures by conventional methods. Here, we report a one-step template-free method to synthesize NaBiF₄:Yb,Er (NBFYE) hollow UCNPs via Ostwald ripening under solvothermal conditions. Moreover, we also elucidate the possible formation mechanism of hollow nanoparticles (HNPs) by studying the growth process of nanoparticles in detail. By changing the contents of polyacrylic acid and H₂O in the reaction system, the central cavity size of NBFYE nanoparticles can be adjusted. Benefiting from the structural characteristics of large internal surface area and high surface permeability, NBFYE HNPs exhibit excellent luminescence properties under 980 nm near-infrared irradiation. Importantly, NBFYE hollow UCNPs can act as self-referenced ratiometric luminescent thermometers under 980 nm laser irradiation, which are effective over a wide temperature range from 223 K to 548 K and have a maximum sensitivity value of 0.0065 K^-1 at 514 K. Our work clearly demonstrates a novel method for synthesizing HNPs and develops their applications, which provides a new idea for constructing hollow structure UCNPs and will also encourage researchers to further explore the optical applications of hollow UCNPs.

Unravelling phase and morphology evolution of NaYbF4 upconversion nanoparticles via modulating reaction parameters

The phase and morphology evolutions of NaYbF4 upconversion nanocrystals have been systemically explored through modulating the experiment parameters in a canonical high-temperature co-precipitation method.

Long-wavelength NIR luminescence of 2,2′-bipyridyl-Pt(ii) dimers achieved by enhanced Pt–Pt interaction

Benefiting from the very strong intermolecular Pt–Pt interaction, 2,2′-bipyridyl-Pt(ii) dimers have achieved long-wavelength near-infrared luminescence exceeding 1000 nm for the first time.